This invention is concerned with improvement of flat optical elements used as Faraday rotators, polarizers and analyzers, and a production method for these optical elements.
Ordinarily, Faraday rotators, polarizers and analyzers are combined as flat optical elements to make up optical devices such as optical isolators, optical regulators, wavelength division multiplexors (WDM), field sensors, optical switches and so on. To improve productivity in the manufacture of these flat optical elements, multiple pieces are obtained by cutting a large piece of optical material that has the characteristics needed for each element.
The flat optical element is made from a large area of flat material which is cut vertically and horizontally, under JPO Kokai Patent S64-79721 (1989), and its shape is square. These square elements do not waste the optical material, all of which is used efficiently.
An optical device constituted by assembling these optical elements has an effective diameter (the device aperture) for incident light and output light, and the flat optical element must be larger than the minimum effective diameter. Therefore, the diagonal measurement of a square element will be 2xc2xd times the minimum effective diameter, and because it is assembled within the inside diameter of a permanent magnet, miniaturization of the optical device is blocked by that structure.
In making up the optical device by assembling these optical elements it is necessary to fix the optical element within the inner diameter of a permanent magnet; fixing with an adhesive or a metal fixture of Au/Sn brazing material. However, because fixing with an adhesive lacks reliability because of such things as deterioration of the adhesive, a metal fixture with brazing material is generally used.
When the four corners are fixed by brazing, the yield of the optical material is liable to drop by reason of cracks which easily form in optical material because there is a difference in the index of thermal expansion of the optical material and the brazing material, and a great difference in area of the fixed portion of one corner and that of the adjacent corner.
Aside from the square elements, there have been proposals such as JPO Patent 2838153 for polygonal flat optical elements with more than 4 sides, such as hexagons or octagons. These shapes are effective for miniaturization of optical devices and for mitigation of the thermal expansion that accompanies brazing.
However, the cutting involved in processing this flat optical material into hexagonal shapes is a time-consuming process, since it is necessary to rotate the large sheet of material repeatedly from 0xc2x0 to 120xc2x0. Moreover, there are more scraps of optical material, and the yield is 60% that of square shapes; the lower yield means higher costs.
Production of octagonal pieces requires a two-step process, first cutting the flat optical material into squares, and then cutting the four corners at a slant. For that reason, the processing is more time-consuming than when hexagonal shapes are processed, and produces more scrap, raising the cost.
The permanent magnets into which the flat optical elements are assembled can be formed with an inner opening that is round, or with a cross-sectional shape that matches the outline of the flat optical element. The octagonal shape has less space between the outline of the element and the inner opening of the permanent magnet, and has the advantage for polarizers and analyzers of a smaller region that does not overlap the beam direction, so that the return beam is blocked fully.
Because of the lesser space between the outline of the element and the inner opening of the permanent magnet, however, the brazing accumulation of these octagonal pieces is inadequate. For this reason, there is the worry of poor fixture of flat optical elements by brazing.
The purpose of this invention is to provide flat optical devices that, because they are nearly octagonal, allow miniaturization of optical devices, and flat optical elements that can be fixed securely within the inner opening of the permanent magnet by brazing.
This invention also has the purpose of providing a method of production of flat optical elements that is capable of efficiently obtaining multiple flat optical elements from a large piece of flat optical material.
The flat optical elements of this invention are formed with nearly octagonal outlines, with sides that are alternately four straight lines and curves.
In the method of producing flat optical elements of this invention, multiple flat optical elements are obtained by making openings that are circular or elliptical in shape at intersections of the cut lines at which the flat optical material is cut vertically and horizontally, cutting the flat optical material in which the openings have been made vertically and horizontally, and obtaining a number of flat optical elements, each with a nearly octagonal outline with sides that are alternately four straight lines and curves.